diff --git a/src/platform/adapters/runtime/shared/node-filesystem-adapter.test.ts b/src/platform/adapters/runtime/shared/node-filesystem-adapter.test.ts
index 80cb16b27c..6fa4c8b266 100644
--- a/src/platform/adapters/runtime/shared/node-filesystem-adapter.test.ts
+++ b/src/platform/adapters/runtime/shared/node-filesystem-adapter.test.ts
@@ -12,6 +12,7 @@ import {
   hasUsableWindowsSnapshotIdentity,
   NodeCompatibleFileSystemAdapter,
   readNodeFileSnapshotWithinLimit,
+  resolveNoFollowFlag,
 } from "./node-filesystem-adapter.ts";
 import { setupNodeFsWatcher } from "./shared-watcher.ts";
 
@@ -39,7 +40,40 @@ function requireExclusiveCreator(adapter: NodeCompatibleFileSystemAdapter) {
   return adapter.createFileBytesExclusive;
 }
 
+describe("resolveNoFollowFlag", () => {
+  it("does not throw when node:fs constants are unavailable (#3661)", () => {
+    // In a browser bundle `nodeFsConstants` is `undefined`. Reading `.O_NOFOLLOW`
+    // off it must degrade to "unavailable", not throw at construction. Passing
+    // `undefined` for `constants` reproduces the non-Node runtime directly.
+    assertEquals(resolveNoFollowFlag({}, undefined), undefined);
+  });
+
+  it("returns the runtime O_NOFOLLOW when the constants are present", () => {
+    assertEquals(resolveNoFollowFlag({}, { O_NOFOLLOW: 0x20000 }), 0x20000);
+  });
+
+  it("lets an own noFollow option win over the runtime constants (test seam)", () => {
+    assertEquals(resolveNoFollowFlag({ noFollow: 7 }, { O_NOFOLLOW: 0x20000 }), 7);
+    // An own `undefined` means "unavailable" even when constants exist.
+    assertEquals(resolveNoFollowFlag({ noFollow: undefined }, { O_NOFOLLOW: 0x20000 }), undefined);
+  });
+});
+
 describe("NodeCompatibleFileSystemAdapter", () => {
+  it("constructs without exact-snapshot support when node:fs constants are absent (#3661)", () => {
+    // Reproduce the browser path end to end: no runtime O_NOFOLLOW available, so
+    // the adapter must construct (not throw) and simply cannot bind an exact
+    // inode snapshot. `noFollow: undefined` is the documented "unavailable" seam.
+    const adapter = new NodeCompatibleFileSystemAdapter(undefined, {
+      noFollow: undefined,
+      platform: "posix",
+    });
+    assertEquals(
+      (adapter as { readFileSnapshotWithinLimit?: unknown }).readFileSnapshotWithinLimit,
+      undefined,
+    );
+  });
+
   it("reads empty and exact-limit snapshots and rejects invalid or oversized inputs", async () => {
     const root = await Deno.makeTempDir({ prefix: "veryfront-node-snapshot-" });
     try {
diff --git a/src/platform/adapters/runtime/shared/node-filesystem-adapter.ts b/src/platform/adapters/runtime/shared/node-filesystem-adapter.ts
index 508e8fda51..cb57e2d6e6 100644
--- a/src/platform/adapters/runtime/shared/node-filesystem-adapter.ts
+++ b/src/platform/adapters/runtime/shared/node-filesystem-adapter.ts
@@ -396,6 +396,25 @@ async function createNodeFileBytesExclusive(
   );
 }
 
+/**
+ * Resolve the `O_NOFOLLOW` open flag that binds an exact-inode snapshot read.
+ *
+ * `constants` is `undefined` in a runtime without `node:fs` — e.g. a browser
+ * bundle that transitively imports this adapter. Dereferencing `.O_NOFOLLOW` on
+ * it unconditionally threw `Cannot read properties of undefined (reading
+ * 'O_NOFOLLOW')` during construction and aborted client hydration (#3661).
+ * Treat the missing constants as "unavailable" (`undefined`) — the same meaning
+ * {@link NodeFileSystemCapabilityOptions.noFollow} already documents for an own
+ * `undefined` — so `canOpenExactSnapshot` degrades to `false` instead of the
+ * constructor exploding. An own `noFollow` on `options` still wins (the test seam).
+ */
+export function resolveNoFollowFlag(
+  options: NodeFileSystemCapabilityOptions,
+  constants: { readonly O_NOFOLLOW?: number } | undefined,
+): number | undefined {
+  return hasOwn(options, "noFollow") ? options.noFollow : constants?.O_NOFOLLOW;
+}
+
 /**
  * Filesystem implementation shared by runtimes that provide Node-compatible
  * `node:fs` APIs (currently Node.js and Bun).
@@ -409,7 +428,7 @@ export class NodeCompatibleFileSystemAdapter implements FileSystemAdapter {
       ...nodeFileSystemOperations,
       ...options.operations,
     } as NodeFileSystemOperations;
-    const noFollow = hasOwn(options, "noFollow") ? options.noFollow : nodeFsConstants.O_NOFOLLOW;
+    const noFollow = resolveNoFollowFlag(options, nodeFsConstants);
     const platform = options.platform ?? (runtimeUsesWindowsPaths() ? "windows" : "posix");
     const canOpenExactSnapshot = platform === "windows"
       ? hasUsableWindowsSnapshotIdentity(detectNodeCompatibleRuntime())